4.0.0 - crash with async I/O and VMDK snapshots => fixed in svn/4.0.2

Description

Hello

i have just upgraded from virtualbox 3.2.12 to 4.0.0
and i can't start my Ubuntu 10.04 machine . it crashes with the following line
" plymouth main process terminated status 2"
and then VirtualBox software crashes also!

This crash will be fixed in 4.0.2. It happens if a VM uses VMDK images, has snapshosts and uses async I/O (default for the SATA controller you are using).
As a workaround, enable "Use host I/O cache" in the controller settings of the VM.

However two things happened which I don't know if related to the workaround
or happened because of the virtual box crash.

After the ubuntu started I tried to install the guest addition from the virtualbox cd. I got many errors that the system disk can't be accessed and its only in read-only mode. then the install failed. and I was only able to shutdown the ubuntu. (no other software work too)

after I closed it , it started only in single mode due to disk errors.

I had to do fsck on the virtual disk and only after that I was able to start
the ubuntu and install the guest addition then update the ubuntu.

Again it might be due to the virtualbox crashing many times in the middle of the
Boot sequence which did something to the virtual disk.

So I tried with/without I/O cache, tried ext3, ext4, ntfs, same issue. I could reproduce the error by logging into the MSDN subscription website and download an ISO. After the download completed, the download tool provided by the msdn subscription site would do a crc check. Sometimes I could get one to suceed, but for the most part a crc error would get thrown. I had this problem running VirtualBox 3.2.8 OSE and 4.0.0. It didn't matter if I ran VirtualBox host as Ubuntu 10.10 or Windows 7. I can't wait to get this bug fixed.